PC Adam Cox, 31, was working in Parliamentary and Diplomatic Protection when he created an alter ego called Emily Whitehouse to exchange explicit sexual chat with three men online.

The crime will also be on your criminal record and you may be required to register as a convicted sex offender.

But the prosecution has the burden of clearly proving your guilt beyond all reasonable doubt.

Creating even the smallest doubt in the minds of the judge and jury can have a profound impact on the final decision.

On being asked to send them sexually revealing photographs, Cox sent images of a Canadian woman who committed suicide at the age of 21, passing them off as “Emily”. I’ve not got a secret stash.”On his Emily persona, he said: “It’s me. It’s madness, a way of escaping reality.”Cox, of Windsor, Berkshire, pleaded guilty at the Old Bailey to four counts of possession of indecent images, including 645 of the most serious category A and 396 extreme pornographic images of bestiality.

Police investigating the Emily online chat raided his home last year. He denied encouraging three men to attempt to get indecent images from “Emily” and the charges were ordered to lie on file.

They found 1,691 indecent and extreme images, including children as young as seven. Prosecutor Charles Falk said Cox had been working for the Metropolitan Police with responsibility for the security of embassies, Parliament and royal family.